From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: alt.engr.explosives
Subject: Confined Explosions
Date: 18 Nov 1995 21:16:34 GMT
Organization: Consulting Chemist
Lines: 109

Sometime ago there was a question posed regarding what would
happen in a super confined explosion.  I've received a reminder
that no one addressed the subject, although the inquiry was
a sincere request for information. The inquiry was sent to
my e-mail address, but I believe the intention was to get this 
discussion into the mainstream conversation. Anyway, here's
the question along with my attempt at an answer: 

>What happens when a HE is immovably confined? Say one had an 
>ounce or two of something strong at the center of a steel sphere thick
>enough to survive detonation, and some way to set off the charge
>without a substantial exit hole, i.e. vanishingly thin wires or some
>such. What would be the result?
>
>Also, can anyone recommend an entertaining book or two about
>explosives (in print), or perhaps other sources? I'm not looking for
>technical manuals, formulae, how to... but rather something anecdotal,
>that describes what happens, accidentally or on purpose, and the
>effects in slow motion detail, for various common and uncommon
>devices. It's a fascinating subject and I'd like to know more...
>
>This is a sincere request for info. What more can I say. I'm not a kid
>(44 years old), but fooled around with dangerous stuff when I was a
>teenager enough to know I'm very lucky.


I remember your message but I was not aware that no one had attempted
to answer it. If you assume that the metal is infinitely strong but  
not a perfect thermal insulator, then the state of the reactants 
immediately after the reaction depends on the initial volume into 
which the charge explodes. I assume that you are probably imagining 
that the condensed charge is packed at its crystal density in the 
metal shell.

If the metal chamber is full of a typical CHNO ezxplosive with a 
perfect oxygen balance, the instantaneous detonation products will 
be CO2, H2O and water vapor at a temperature of several thousand 
degrees centigrade. The exact temperature for any know explosive 
before the expansion phase is debatable. Cook mentions attempts to 
peer into the detonation front of nitroglycerin, using plexiglas 
rods. The spectra of the emitted light suggest a temperature in the 
5-6,000 deg C range, but no one is certain that luminous effects 
from the shockwave entering the plexiglas are not producing 
contributory light effects. Cook even suggests that the concept of   
"temperature" may be misleading when applied to a high pressure 
explosive plasma.

At any rate, the pressure in a detonation front of a good military 
class explosive is on the order of 4 million psi and that figure 
would be the same in the metal container at the the moving 
detonation head, and higher in the reflected shocks from the 
unyielding surfaces. However, I would expect the AVERAGE pressure, 
before cooling has time to set in, to be considerably lower than 
the 4,000,000 psi figure because the  detonation occurs in a moving
band of matter precompressed by the shock front.

As the metal container conducts heat away from the reaction products, 
first the water and then the CO2 would condense, the former at or 
below its critical temperature of 374 deg C, depending on the 
quantity of water produced. The CO2 would begin condensing shortly 
after the water by dissovling therin and ultimately produce truly 
"pin-point" carbonation :) In the absence of water, the CO2 would 
remain gaseous right down to 31 deg C.  The product nitrogen, being 
a permanent gas, would not condense.

The state of our cooled products depends greatly on the composition
of the original explosive. Let's choose as an example a real-life 
oxygen-balanced species: one gram of ethyleneglycol dinitrate. 
C2N2H4O6, FW = 152.1.

C2N2H4O6 --> 2CO2 + 2H2O + N2 

The density is about 1.49 so the metal cavity must have a volume of 
1/1.49 = 0.671 ml.

The water produced is 2*18.02/152.1 = 0.237 g or about the same 
number of mls.

The CO2 weighs  2*44.01/152.1 = 0.579g

I have no density data for CO2 at ambient temperatures, but it is 
obviously less than the 1.1 g/ml reported at - 27 deg;; therefore 
the volume at room temperature must be greater than 0.579/1.1 or 
>>0.526 ml.

Thus, it appears that that the sum of the NORMAL volumes of the 
liquids in the cold reaction products is greater than 0.526 + 0.237 
= 0.763 ml which is crammed into a 0.671  ml cavity in the metal 
along with 1/152.1 moles of gaseous N2, which would exert an ideal 
pressure at 293 deg K of 1/152*22,414* 1/0.671*293/273 = 235 atm 
if it had the entire volume to itself, rather than just the tiny 
intermolecular spaces between already very highly compressed CO2, 
H2O and H2CO3 molecules in the liquid state.  

Without the probably enormous pressure attributable to the 
super-compressed nitrogen in this scenario, the hydrostatic pressure 
of the liquids alone would likely excede 5,000 atm, assuming 
compressibility comparable to that of water.

In short, the final, cold reaction products would be under enormous 
and difficultly calculable pressure, probably in excess of anything 
real metal could take.

I rarely string more than a few figures together without a mistake, 
so feel free to ferret out the errors.

Jerry